1. Field of the Invention
The present invention relates to a method for manufacturing a coating rod for coating various types of liquid materials (coating liquids) on a continuously traveling sheet-like or belt-like substrate (hereinafter referred to as a web), such as a thin metal sheet, paper or film, and smoothing the liquid material after coating.
2. Description of the Related Art
As coating apparatuses for coating various types of coating liquids on a web, such as a thin metal sheet, paper, or a plastic film, there is known a variety of apparatus, including a roll coater, an air knife coater, a coater using dies, and a rod coater.
Of these coating apparatuses, the rod coater is a simple coating apparatus capable of coating various types of coating liquids on various types of webs, and therefore, is widely utilized. The rod coater includes a type which scrapes off excess amounts of coating liquid coated on the web with a coating rod (also referred to as a coating bar), and a type which performs both coating on the web and adjustment of the amount of coating liquid with one coating rod. In either type of rod coater, a multitude of grooves is formed on a surface of the coating rod in the circumferential direction thereof. By adjusting the depth and width of these grooves, the amount of coating liquid coated on the web and the amount of coating liquid to be scraped off are adjusted.
As a method for forming grooves on the surface of the coating rod, there is known a method of groove formation by means of form rolling. In this method, a rod material is held between two form rolling dies in which grooves are formed. The rod material is advanced in the axial direction thereof, while rotating the form rolling dies, thereby forming grooves on a surface of the rod material. This method has the problem, however, that if the depth of grooves formed on the rod material is non-uniform due to uneven form rolling, the highest portion of the rod material locally has contact with the web, thus producing scratches.
In order to solve this problem, Japanese Patent No. 4460257 discloses a method for grinding surfaces (ridges) of a coating rod after form rolling, so that 99.5% or more of the cross sections of ridges orthogonal to the axial direction of the coating rod are flush with one another.
In the method disclosed in Japanese Patent No. 4460257, however, ridges are ground after form rolling out of consideration of the shape of valleys. Accordingly, the cross-sectional area of each groove may change due to grinding, thus causing uneven coating in some cases.
The present invention has been accomplished in view of such circumstances, and an object of the invention is to provide a method for manufacturing a coating rod capable of eliminating scratches and uneven coating on a web.